Secondary charged particle imaging system

ABSTRACT

A secondary charged particle imaging system comprising: a backscattered electron detector module, wherein the backscattered electron detector module is rotatable between a first angular position and a second angular position about an axis.

Aspects of the disclosure relate to scanning charged particle beamdevice, particularly for image generation on a specimen. Aspects relatein particular to a secondary charged particle imaging system. Anotheraspect relates to a scanning electron microscope including thebackscattered electron detector module. A further aspect relates to amethod of operating a secondary charged particle imaging system.

TECHNICAL BACKGROUND

Charged particle beam apparatuses have many functions in a plurality ofindustrial fields, including, but not limited to, inspection ofsemiconductor devices during manufacturing, exposure systems forlithography, detecting devices and testing systems. Thus, there is ahigh demand for structuring and inspecting specimens within themicrometer and nanometer scale.

Micrometer and nanometer scale process control, inspection orstructuring, is often done with charged particle beams, e.g. electronbeams, which are generated and focused in charged particle beam devices,such as electron microscopes or electron beam pattern generators.Charged particle beams offer superior spatial resolution compared to,e.g. photon beams due to their short wavelengths.

Charged particle beam apparatuses typically make use of a chargedparticle imaging system. A charged particle imaging system may beconfigured for single-beam or multi-beam imaging. The followingdescribes a charged particle imaging system with improved performance.

SUMMARY

In view of the above, provided are a secondary charged particle imagingsystem, a charged particle beam device, and a method of operating asecondary charged particle imaging system.

According to one aspect, a secondary charged particle imaging system,the secondary charged particle imaging system including a backscatteredelectron detector module, and wherein the backscattered electrondetector module is rotatable between a first angular position and asecond angular position about an axis.

According to one aspect, a charged particle beam device including thesecondary charged particle imaging system.

According to one aspect, a method of operating the secondary chargedparticle imaging system including rotating the backscattered electrondetector between a first angular position and a second angular positionabout an axis.

Further advantages, features, aspects and details that can be combinedwith embodiments described herein are evident from the dependent claims,the description and the drawings.

BRIEF DESCRIPTION OF THE FIGURES

The details will be described in the following with reference to thefigures, wherein:

FIG. 1 is a simplified side view schematic of a secondary chargedparticle imaging system according to embodiments described herein,

FIG. 2 is a simplified top view schematic of a secondary chargedparticle imaging system according to embodiments described herein,

FIG. 3 is a simplified side view schematic of a backscattered electrondetector module and a backscattered electron detector actuator moduleaccording to embodiments described herein,

FIGS. 4A and 4B are simplified pseudo-3D representations of an arm witha mechanical hinge joint, the arm being of a backscattered electrondetector module according to embodiments described herein,

FIGS. 5A and 5B are simplified side view schematics of the backscatteredelectron detector module in a first angular position and second angularposition according to embodiments described herein,

FIGS. 6A and 6B are close-up simplified side view schematics of theaperture and backscattered electron detector element of thebackscattered electron detector module in a first angular position andsecond angular position according to embodiments described herein,

FIG. 7 is a simplified side view schematic of a charged particle beamdevice according to embodiments described herein, and

FIG. 8 is a method diagram for operating a secondary charged particleimaging system according to embodiments described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to the various embodiments, one ormore examples of which are illustrated in each figure. Each example isprovided by way of explanation and is not meant as a limitation. Forexample, features illustrated or described as part of one embodiment canbe used on or in conjunction with any other embodiment to yield yet afurther embodiment. It is intended that the present disclosure includessuch modifications and variations.

Within the following description of the drawings, the same referencenumbers refer to the same or to similar components. Generally, only thedifferences with respect to the individual embodiments are described.Unless specified otherwise, the description of a part or aspect in oneembodiment applies to a corresponding part or aspect in anotherembodiment as well.

The reference numbers used in the figures are merely for illustration.The aspects described herein are not limited to any particularembodiment. Instead, any aspect described herein can be combined withany other aspect(s) or embodiment(s) described herein unless specifiedotherwise.

FIG. 1 shows a simplified side view schematic of a secondary chargedparticle imaging system. According to embodiments described herein, thesecondary charged particle imaging system includes a backscatteredelectron detector module.

The backscattered electron detector module 1400 may be configured tocollect and/or detect backscattered electrons, e.g. on-axialbackscattered electrons, in an electron beam column. For example, thebackscattered electrons can be backscattered electrons of a signalcharged particle beam 1102. The backscattered electron detector module1400 may be configured to allow the signal charged particle beam 1102 topass through. According to embodiments, the backscattered electrondetector module 1400 may be configured to be moveable and/or rotatable,such as between a first position 5452 and a second position 5454. Thefirst position 5452 and second position 5454 may be angular positions.In an example, the backscattered electron module 1400 may be configuredto allow the signal charged particle beam 1102 to pass through thebackscattered electron module in the first position 5452. Thebackscattered electron module 1400 may be configured to collect and/ordetect backscattered electrons and/or signals in the signal chargedparticle beam 1102 in the second position 5454.

Accordingly, the backscattered electron detector module 1400 may includean aperture 1460. The backscattered electron detector module 1400 mayinclude a backscattered electron detector element 1470. The aperture1460 and the backscattered electron detector element 1470 may bearranged on a backscattered electron detector holder 1450. The aperture1460 and the backscattered electron detector element 1470 may bearranged in a plane or in planes parallel to each other. For example,the backscattered electron detector element 1470 is supported on thebackscattered electron detector holder 1450 and the aperture 1460 isformed in the backscattered electron detector holder 1450. In anotherexample, the aperture 1460 may be fixed in a position on the opticalaxis 1103 and the backscattered electron detector holder 1450 ismoveable between the first position 5452 and the second position 5454.The optical axis 1103 is an optical axis of the signal charged particlebeam 1102. In a preferred embodiment, the aperture 1460 is arranged onthe optical axis 1103 and the backscattered electron detector element1470 is arranged off the optical axis 1103 when the backscatteredelectron detector module 1400 is in the first position 5452. In thepreferred embodiment, the backscattered electron detector element 1470is arranged on the optical axis 1103 and the aperture 1460 is arrangedoff the optical axis 1103 when the backscattered electron detectormodule 1400 in the second position 5454. The phrase ‘on the opticalaxis’ may be understood as a position that is at least partially,preferably substantially, overlapping or coinciding with a position ofthe signal charged particle beam 1102. The phrase ‘off the optical axis’may be understood as a position that is at least partially, preferablysubstantially, and even more preferably completely, distinct or notoverlapping with a position of the signal charged particle beam 1102.

According to one embodiment, the backscattered electron detector module1400 includes the backscattered electron detector element 1470 and theaperture 1460. Alternatively, the aperture 1460 may be replaced by arecess or the backscattered electron detector module 1400 may bemoveable by an angle sufficiently large that the signal electrons orsignal charged particle beam 1102 can pass next to the backscatteredelectron detector module 1400.

In embodiments, there may be a secondary charged particle optics moduleand/or a beam bender. The backscattered electron detector module 1400may be arranged before the secondary charged particle optics module 1600and/or after the beam bender 1392. For example, the backscatteredelectron detector module 1400 may be arranged between the secondarycharged particle optics module 1600 and the beam bender 1392. Thebackscattered electron detector module 1400, the aperture 1460 and/orthe backscattered electron detector element 1470 may be arranged afteror downstream of the beam bender 1392. The backscattered electrondetector module may be arranged immediately or directly after ordownstream of the beam bender. The backscattered electron detectorelement 1470 and/or the aperture 1460 may be arranged before or upstreamof the secondary charged particle optics module 1600. The backscatteredelectron detector module may be arranged immediately or directly beforeor upstream of the secondary charged particle optics module 1600.‘After/before’ and/or ‘downstream/upstream’ can be understood withrespect to the propagation of the signal charged particle beam 1102. Forexample, ‘downstream’ may understood to be similar to ‘after’ and viceversa, ‘upstream’ to be similar to ‘before’.

Accordingly, in an example, the secondary charged particle optics module1600 and/or the aperture 1460 is in a functional position in the firstposition 5452. In another example, the signal charged particle beam 1102passes through the backscattered electron detector module 1400 in thefirst position 5452. Similarly, in a further example, the backscatteredelectron detector module 1400 and/or the backscattered electron detectorelement 1470 is in a functional position in the second position 5454. Inyet another example, the signal charged particle beam 1102 isintercepted and/or detected by the backscattered electron detectormodule 1400 and/or the backscattered electron detector element 1470 inthe second position 5454. Accordingly, in an example, the secondarycharged particle optics module 1600, the aperture 1460, and the beambender 1392 are arranged, particularly in that order, on the opticalaxis 1102 in the first position 5452. In another example, the secondarycharged particle optics module 1600, the backscattered electron detectorelement 1460, and the beam bender 1392 are arranged, particularly inthat order, on the optical axis 1102 in the second position 5454. Inembodiments, that can be combined with other embodiments describedherein, the backscattered electron detector module 1400 and/or thebackscattered electron detector element 1470 may be arrangeable at oradjacent to a point of the smallest cross-section of the signal chargedparticle beam 1102. A point of the smallest cross-section of the signalcharged particle beam 1102 may be after or downstream of the beam bender1392, in particular immediately after the beam bender 1392. Inembodiments, it is considered beneficial to arrange the backscatteredelectron detector module 1400 and/or the second lens 1616 as close aspossible to the beam bender 1392.

The arrangement of the backscattered electron detector module 1400, suchas the backscattered electron detector element 1470, as described above,can provide a good performance of backscattered electron efficiency. Forexample, detection efficiency can be improved by up to 30% compared toarranging the backscattered electron detector module 1400, such as thebackscattered electron detector element 1470, after or downstream of thesecondary charged particle optics module 1600.

FIG. 1 shows a simplified side view schematic of a secondary chargedparticle imaging system. According to embodiments described herein, thesecondary charged particle imaging system includes a beam bender.

The beam bender 1392 may be for bending the signal charged particle beam1102. The beam bender 1392 may have a shape or cross-section of asector, in particular a hemispherical sector. The beam bender 1392 maybe configured for changing the direction of the signal charged particlebeam 1102 so that the travel direction of the signal charged particlebeam 1102 entering the beam bender 1392 is different when compared tothe travel direction of the signal charged particle beam 1102 leavingthe beam bender 1392. The beam bender 1392 may be arranged to direct thesignal charged particle beam 1102 further away from a primary chargedparticle beam 7101. For example, the beam bender 1392 may deflect thesignal charged particle beam 1102, in particular by electrostatic means.The beam bender 1392 may be arranged downstream of a means of beamseparation. Beam separation may be understood as a means to separate aprimary charged particle beam from a secondary charged particle beam. Asecondary charged particle beam 1102 may be understood as a chargedparticle beam originating from a sample 7350. A primary charged particlebeam 7101 may be understood as a charged particle beam that impinges ona sample 7350. The beam bender may be a spherical or sector beambenders. The beam bender 1392 may deflect and/or stigmatically focus acharged particle beam.

In embodiments, the beam bender 1392 acting on the signal chargedparticle beam 1102 is arranged, with respect to the signal chargedparticle beam 1102, upstream of the second lens 1616. In the drawingplane of FIG. 1, the beam bender 1392 is arranged to the right of thesecond lens 1616. As shown, the signal charged particle beam 1102 entersthe beam bender 1392 from below and travels through the beam bender1392. The signal charged particle beam 1102 exiting the beam bendertravels along a substantially horizontal direction. The signal chargedparticle beam 1102 may travel from the beam bender 1392 to the secondlens 1616 of the lens system 1610. As illustrated in FIG. 1, the secondlens 1616 may be arranged, with respect to the signal charged particlebeam 1102, downstream of the beam bender 1392, and/or the backscatteredelectron detector module 1400. In a preferred embodiment, the secondlens 1616 may be the next element acting on the signal charged particlebeam 1102 leaving the backscattered electron detector module. An openingangle of the secondary charged particle beam, as described herein, maybe an opening angle of the signal charged particle beam exiting the beambender 1392.

FIG. 1 shows a simplified side view schematic of a secondary chargedparticle imaging system. According to embodiments described herein, thesecondary charged particle imaging system includes a secondary chargedparticle optics module.

In embodiments, the secondary charged particle optics module 1600includes a lens system 1610. The lens system 1610 may include a firstlens 1612 and a second lens 1616. The first lens 1612 may be distancedfrom the second lens 1616. For example, the distance between the firstlens 1612 and the second lens 1616 may be in the range from 40 to 200mm.

With respect to the drawing plane of FIG. 1, the first lens 1612 and/orthe second lens 1616 extend along a vertical (“up-down”) direction. Thefirst lens 1612 may be arranged between the aperture plate 1650 and thesecond lens 1616.

In the drawing plane of FIG. 1, the signal charged particle beam 1102travels from right to left. The signal charged particle beam 1102 entersthe second lens 1616 of the lens system 1610 from the right-hand side ofthe second lens 1616. The signal charged particle beam 1102 shown inFIG. 1 travels through the second lens 1616 and subsequently through thefirst lens 1612 of the lens system 1610. As shown, the signal chargedparticle beam 1102 traveling through the lens system 1610 travelssubstantially along the optical axis 1103.

The first lens 1612 and/or the second lens 1616 may be adapted forshaping, focusing and/or defocusing the signal charged particle beam1102. The first lens 1612 and/or the second lens 1616 may be adapted foradjusting an opening angle of the signal charged particle beam 1102. Thesignal charged particle beam 1102 can be made divergent or convergent asdesired. Accordingly, collection efficiency of signal charged particlesby the detector arrangement 1900 can be improved. An opening angle ofthe signal charged particle beam 1102 may be an opening angle of thesignal charged particle beam 1102 exiting a beam bender arrangedupstream, with respect to the propagation of the signal charged particlebeam 1102, of the lens system 1610.

The lens system 1610 may be adapted for providing one or two cross-oversof the signal charged particle beam 1102. Alternatively, the lens system1610 may be adapted for allowing the signal charged particle beam topass through the lens system 1610 without a cross-over.

The first lens 1612 may include an electrostatic lens portion and/or amagnetic lens portion. The first lens 1612 may be a compound lensincluding both an electrostatic lens portion and a magnetic lensportion. Similarly, the second lens 1616 may include an electrostaticlens portion and/or a magnetic lens portion. An electrostatic lensportion of the first lens 1612 and/or an electrostatic lens portion ofthe second lens 1616 may be adapted for shaping, focusing and/ordefocusing the signal charged particle beam. A magnetic lens portion ofthe first lens 1612 and/or of the second lens 1616 may be adapted forcompensating a Larmor rotation of an objective lens.

It is considered beneficial to arrange the second lens 1616 as close aspossible to the backscattered electron detector module 1400 and/or thebeam bender 1392. It is also considered beneficial to arrange the firstlens 1612 sufficiently far away from the beam bender 1392. According toembodiments, which can be combined with other embodiments describedherein, the distance between the backscattered electron detector module1400 and the second lens 1616 is 60 mm or below, in particular 45 mm orbelow, more particularly 35 mm or below. According to embodiments, whichcan be combined with other embodiments described herein, the distancebetween the beam bender 1392 and the first lens 1612 is 50 mm or above,more particularly 100 mm or above, for example 115 mm or above.

The first lens 1612 may include a first magnetic lens portion 1614adapted for generating a magnetic field. The first magnetic lens portion1614 may include a coil for generating the magnetic field. The firstmagnetic lens portion 1614 may have an iron cladding. Similarly, thesecond lens 1616 may include a second magnetic lens portion 1618. Thesecond magnetic lens portion 1618 may include similar componentscompared to the first magnetic lens portion 1614. The first magneticlens portion 1614 and/or the second magnetic lens portion 1618 may beadapted for compensating a Larmor rotation of the signal chargedparticle beam 1102. The Larmor rotation may be introduced in the signalcharged particle beam 1102 due to a variation of the strength of amagnetic field generated by the objective lens of the charged particlebeam device, e.g., a magnetic field (not shown in FIG. 1). The firstmagnetic lens portion 1614 and/or the second magnetic lens portion 1618may be adapted for rotating the signal charged particle beam 1102. Therotation of the signal charged particle beam 1102 may be a rotationaround the optical axis 1103 defined by the aperture plate 1650 and maybe a clock-wise or a counter-clockwise rotation. The first magnetic lensportion 1614 may be adapted for rotating the signal charged particlebeam 1102 by a first angle A1. The first angle A1 may lie in the rangefrom −45 to 45 degrees. Accordingly, a Larmor rotation from −45 to 45degrees can be compensated by the first magnetic lens portion. Thesecond magnetic lens portion 1618 may be adapted for rotating the signalcharged particle beam 1102 by a second angle A2. The second angle A2 maylie in the range from −45 to 45 degrees. Accordingly, a Larmor rotationfrom −45 to 45 degrees can be compensated for by the second magneticlens portion. A lens system where the first lens includes a firstmagnetic lens portion and the second lens includes a second magneticlens portion, such as e.g. the lens system 1610 shown in FIG. 1, may beadapted for rotating the signal charged particle beam by a total anglelying in the range from −|A1|−|A2| to |A1|+|A2| where |A1| and |A2|denote the absolute values of A1 and A2, respectively. Accordingly, aLarmor rotation lying in the range from −|A1|−|A2| to |A1|+|A2| can becompensated for by the lens system. For example, a Larmor rotationbetween −90 and 90 degrees can be compensated for.

An advantage of compensating the Larmor rotation of the signal chargedparticle beam with a first magnetic lens portion included in the firstlens and/or a second magnetic lens portion included in the second lensis that no mechanical rotation of the aperture plate and/or the detectorarrangement for compensating the Larmor rotation is required.

The first lens 1612 may be a compound lens including an electrostaticlens portion (not shown) and a first magnetic lens portion 1614.Compared to a first lens including an electrostatic lens portion but nofirst magnetic lens portion, a compound lens provides additional degreesof freedom for influencing the secondary charged particle beam. Inparticular, two such additional degrees of freedom provided by a firstmagnetic lens portion 1614 may include the magnitude and direction of acurrent passed through a coil included in the first magnetic lensportion 1614. Similar considerations apply to embodiments where thesecond lens is a compound lens.

The magnetic field generated by the first magnetic lens portion 1614 mayaffect the focusing of the signal charged particle beam 1102 onto theaperture plate 1650. Such a focusing effect may be compensated for orfurther enlarged by setting the excitation of the electrostatic lensportion of the first lens 1612 to an appropriate value. For example, thefocusing effect may be affected by reducing or increasing the refractivepower of the electrostatic lens portion. Accordingly, the signal chargedparticle beam 1102 may be shaped, focused and/or defocused in a desiredmanner. Accordingly, via a combined action of the first magnetic lensportion 1614 and the electrostatic lens portion, the first lens 1612 maybe configured to compensate a Larmor rotation of the objective lensand/or shape, focus and/or defocus the signal charged particle beam1102. Similar considerations apply to embodiments where the second lensis a compound lens.

As an alternative to the illustration of FIG. 1 where both the firstlens 1612 and the second lens 1616 include a magnetic lens portion,according to other embodiments described herein, it may be that only oneof the first lens 1612 and the second lens 1616 includes a magnetic lensportion for compensating the Larmor rotation. According to embodiments,at least one of the first lens and second lens comprises a magnetic lensportion for compensating the Larmor rotation of the objective lens.

According to yet further embodiments, which can be combined with otherembodiments described herein, the first lens and second lens comprise orconsist of an electrostatic lens portion. For example, the first lensand second lens do not comprise a magnetic lens portion. As an optionalmodification, particularly for such embodiments, a Larmor rotation canbe provided or compensated by a coil, e.g. a Larmor rotation coil. Forexample, the Larmor rotation coil can be downstream of the first lensand/or second lens.

According to embodiments, the secondary charged particle optics module1600 may include a controller 1630. The controller 1630 shown in FIG. 1may be configured for controlling the excitation of the first lens 1612and the excitation of the second lens 1616. Controlling the excitationof the first lens 1612 may include controlling the excitation of anelectrostatic lens portion of the first lens 1612 and/or controlling theexcitation of a magnetic lens portion of the first lens 1612. Similarconsiderations apply to the case where the second lens 1616 includes anelectrostatic and/or magnetic lens portion.

An electrostatic lens portion of the first lens 1612 may include one ormore electrodes for generating an electric field. A potential may beapplied to the electrodes for generating the electric field. Theelectric field may be generated under the control of the controller1630. In particular, the strength of the electric field may becontrolled by, determined by and/or adjusted under the control of thecontroller 1630. A magnetic lens portion of the first lens 1612 may eachinclude one or more coils for generating a magnetic field. A current maybe passed through the coils for generating the magnetic field. Themagnetic field may be generated under the control of the controller1630. In particular, the strength of the magnetic field as well as thefield direction determined by the current direction through the coilsmay be controlled by, determined by and/or adjusted under the control ofthe controller 1630. Similar considerations apply to an electrostaticlens portion and/or magnetic lens portion included in the second lens1616. According to embodiments described herein, the first lens mayinclude an electrostatic lens portion, a magnetic lens portion, or both,an electrostatic lens portion and a magnetic lens portion. According toembodiments described herein, the second lens may include anelectrostatic lens portion, a magnetic lens portion, or both, anelectrostatic lens portion and a magnetic lens portion. Providing acombined electrostatic magnetic lens for the first and/or second lens,i.e. having an electrostatic lens portion and a magnetic lens portion,may allow for increased degrees of freedom in adjusting the signalcharged particle beam, particularly with respect to Larmor rotation.

The controller 1630 may be configured for independently controlling theexcitation of the first lens 1612 and of the second lens 1616.Accordingly, the controller 1630 may allow controlling the focusing,defocusing and/or shaping of the signal charged particle beam 1102 bythe first lens 1612 independently of controlling the focusing,defocusing and/or shaping of the signal charged particle beam 1102 bythe second lens 1616. Independently controlling the excitations of thefirst lens 1612 and of the second lens 1616 provides that, in thetopography detection mode of the secondary charged particle imagingsystem, a first sub-beam of the signal charged particle beam 1102 passesthrough the first opening 1653 and is detected by the first detectionelement 1970, that a central sub-beam of the signal charged particlebeam 1102 passes through the central opening 1655 and is detected by thecentral detection element 1950, and that a second sub-beam of the signalcharged particle beam 1102 passes through the second opening 1657 and isdetected by the second detection element 1930.

According to embodiments, which can be combined with other embodimentsdescribed herein, the controller 240 may be configured to switch betweenthe topography detection mode and the bright-field detection mode byadapting the excitations of the first lens 1612 and of the second lens1616. At a first moment in time, the excitations of the first lens 1612and of the second lens 1616 may be set to a first configuration underthe control of the controller 1630 to image the signal charged particlebeam 1102 in the topography detection mode. At a second, e.g. later,moment in time, the excitations of the first lens 1612 and of the secondlens 1616 may be set to a second configuration under the control of thecontroller 1630 to image the signal charged particle beam 1102 in thebright field detection mode. Accordingly, the flexibility of the systemis enhanced.

According to embodiments, which can be combined with other embodimentsdescribed herein, the secondary charged particle imaging system may beconfigured to switch between a secondary charged particle detection modeand a backscattered electron detection mode by rotating thebackscattered electron detector module 1400 between the first position5452 and the second position 5454 respectively. Accordingly, theflexibility of the system is further enhanced.

An advantage of having a controller configured for switching between thetopography detection mode and the bright field detection mode, comparedto a system configured for operating solely according to eithertopography detection mode or according to the bright field detectionmode, is that multiple aspects of the sample, relating to e.g.topography information, defects on the sample, chemical constituents ofthe sample, and the like, can be analysed by a single system.

FIG. 1 shows a simplified side view schematic of a secondary chargedparticle imaging system. According to embodiments described herein, thesecondary charged particle imaging system includes an aperture plate.

The aperture plate 1650 may include a first opening 1653, a centralopening 1655 and/or a second opening 1657. The first opening 1653 may bedistanced from the second opening 1657. The aperture plate 1650 may bearranged parallel to and/or distanced from the first lens 1612 and/or tothe second lens 1616. The first opening 1653 may be formed, with respectto the vertical direction, at an upper portion of the aperture plate1650. The central opening 1655 may be formed at a central portion of theaperture plate 1650. The second opening 1657 may be formed at a lowerportion of the aperture plate 1650. The aperture plate 1650 may definean optical axis 1103. In an example, the distance between the centre ofthe aperture plate 1650 and the centre of the first lens 1612 may be inthe range from 40 to 200 mm.

The aperture plate 1650, the first lens 1612 and/or the second lens 1616may be parallel to a plane defined by the detector arrangement 1900.

In addition to the first opening 1653, the central opening 1655, and thesecond opening 1657, the aperture plate 1650 may include furtheropenings. For example, the aperture plate 1650 can include fiveopenings. The first opening 1653, the second opening 1657 and anyfurther openings may be located around the optical axis 1103 such thatthe aperture plate 1650 has a four-fold rotational symmetry with respectto the optical axis 1103. The first opening 1653, the second opening1657 and any further openings may be radially outward openings withrespect to the optical axis 1103. In an example, the diameter or thecorresponding dimension of the central opening 1655 may be 1 mm to 4 mm.In another example, the first opening 1653, the second opening 1657and/or the further openings may have a diameter or a correspondingdimension in a range from 3 mm to 15 mm. In yet another example, thedistance between the centre of the first opening and the centre of thesecond opening may be in the range from 4 to 15 mm.

The aperture plate 1650 may comprise an integer number N of furtheropenings, wherein the first opening 1653, the second opening 1657 andthe N further openings are located around the optical axis 1103 of theaperture plate 1650 such that the aperture plate 1650 has an N+2-foldrotational symmetry with respect to the optical axis 1650 of theaperture plate 1650.

In a yet further example, the aperture plate may have a thickness of 5mm or above, more particularly the thickness may be from 10 mm to 20 mm.The thickness of the aperture plate may be a thickness in an axialdirection of the aperture plate and/or in a direction parallel to theoptical axis defined by the aperture plate. Having a thickness from 10mm to 20 mm may provide an increased separation of the sub-beams of thesignal charged particle beam. The increased separation allows for theutilization of a detector arrangement where the detection elements, e.g.the first detection element, the second detection element and/or thecentral detection element, may be standard pin diodes with a 5 mmdiameter. Accordingly, a feasible design of the detector arrangement maybe provided. Further, in light of the fact that the reach-through of anacceleration field generated between the aperture plate and the detectorarrangement is influenced by the thickness of the aperture plate, areduced operating voltage is a beneficial side effect from having aminimum thickness of the aperture plate of at least 5 mm. Accordingly,better high voltage immunity, reliability and stability may be provided.

With respect to the propagation of the secondary charged particle beam,the aperture plate is arranged upstream of the detector arrangement.

FIG. 1 shows a simplified side view schematic of a secondary chargedparticle imaging system. According to embodiments described herein, thesecondary charged particle imaging system includes one or moredeflection elements.

The one or more deflection elements may be configured for influencingthe signal charged particle beam 1102. By providing one or moredeflection elements, the information carried by the signal chargedparticles is more easily conserved as the signal charged particle beam1102 is transferred from the sample to the detector arrangement 1900. Asshown, a first deflection element 1720 and a second deflection element1710 may be arranged between the beam bender 1392 and the detectorarrangement 1900. According to alternative embodiments, the secondarycharged particle imaging system may include the first deflection element1720 without the second deflection element 1710 or vice versa, or mayinclude additional deflection elements arranged between the beam bender1392 and the detector arrangement 1900. A third deflection element (notshown) may be provided between the beam bender 1392 and the second lens1616. Alternatively, a third deflection element may be providedupstream, with respect to the signal charged particle beam 1102, of thebeam bender 1392. For example, a third deflection element may beprovided between a beam separator, as described herein, and the beambender. A third deflection element improves alignment and/or imaging ofthe signal charged particle beam on the detector arrangement.Accordingly, signal generation, and thus contrast, can be improved. Theimproved signal generation results in better throughput, particularlyfor EBI applications. The third deflection element may be the nextdeflection element through which the signal charged particle beam 1102leaving the beam bender 1392 passes. The third deflection element may bearranged directly downstream, with respect to the signal chargedparticle beam 1102, of the beam bender 1392 or the backscatteredelectron detector module 1400. Alternatively, the third deflectionelement may be provided between the first lens 1612 and the detectorarrangement 1900. Providing the third deflection element between thebeam bender and the second lens or between the first lens and thedetector arrangement, as described above, has the advantage that apotential space restriction for a third deflection element is not ascritical as compared to e.g. a third deflection element being positionedbetween a beam separator and the beam bender (insufficient separationbetween signal charged particle beam and primary charged particle beam).Arranging the third deflection element between a beam separator and thebeam bender may provide an improved anti-scanning of the signal chargedparticle beam. In particular, deviations of the signal charged particlebeam emanating from an off-axial position with respect to the axis of asignal charged particle beam starting in the centre of the field of viewmay be more easily compensated for.

As shown in FIG. 1, the second deflection element 1710 may be arrangedbetween the first lens 1612 and the second lens 1616. The seconddeflection element 1710 may influence the signal charged particle beam1102 traveling from the second lens 1616 to the first lens 1612. Thefirst deflection element 1720 may be arranged between the aperture plate1650 and the first lens 1612. The first deflection element 1720 mayinfluence the signal charged particle beam 1102 traveling from the firstlens 1612 to the aperture plate 11650. The first deflection element 1720and/or the second deflection element 1710 may be aligned to the opticalaxis 1103, as illustrated in FIG. 1. The optical axis 1103 may extendlongitudinally through the first deflection element 1720 and/or throughthe second deflection element 1710.

A deflection element for influencing the signal charged particle beam,such as e.g. the first deflection element 1720 and/or the seconddeflection element 1710 shown in FIG. 1, may include an electrostaticdeflection portion and/or a magnetic deflection portion. Anelectrostatic deflection portion may include an electrostatic dipole,quadrupole or higher order multi-pole element. A magnetic deflectionportion may include a magnetic dipole, quadrupole or higher ordermulti-pole element. A deflection element may include two deflectionplates arranged on opposite sides of the optical axis defined by theaperture plate and/or arranged on opposite sides of the signal chargedparticle beam. For deflection in two directions, two perpendiculardipole fields may be provided or two deflectors may be provided that maybe operated to allow for one dipole field, which can be rotateddepending on the operation of the two deflectors. For example,individual fields of the two deflectors separately can enclose an angleof 70° to 110°, such as 90°. As shown in FIG. 1, the first deflectionelement 1720 and/or the second deflection element 1710 may each includetwo deflection plates for deflecting the signal charged particle beam ina first direction.

A deflection element for influencing the signal charged particle beammay be adapted to align the signal charged particle beam with theoptical axis of the aperture plate, e.g. in the bright field detectionmode. Additionally, or alternatively, a deflection element, e.g. a thirddeflection element as described herein, may be adapted for anti-scanningthe signal charged particle beam. The signal charged particle beam maybe anti-scanned in a charged particle beam device where the primarycharged particle beam is scanned over a sample. Scanning the primarycharged particle beam over the sample may provide an unwanted deflectionof the signal charged particle beam, wherein the position of the signalcharged particle beam impinging onto the detector arrangement and/or theposition of the signal charged particle beam with respect to theaperture plate may depend on the primary charged particle beam positionbeing scanned over the sample. This dependence may lead to a poordetection quality and a blurred image. Anti-scanning of the signalcharged particle beam, e.g. by the first deflection element 1720 and/orby the second deflection element 1710 shown in FIG. 1, may compensatefor the deflection of the signal charged particle beam resulting fromscanning the primary charged particle beam and/or may align the signalcharged particle beam with a target axis, e.g. the optical axis definedby the aperture plate, independent of the position of the primarycharged particle beam being scanned over the sample. Accordingly,off-axis aberrations of the signal charged particle beam may be avoided.Anti-scanning of the signal charged particle beam may be particularlybeneficial for a charged particle beam device having a large field ofview. According to embodiments, which can be combined with otherembodiments described herein, the field of view of the charged particlebeam device may be 500 μm or above.

To provide an anti-scanning of the signal charged particle beam with adeflection element, a deflection voltage may be applied to thedeflection element. The deflection voltage may be synchronized with thescanning of the primary charged particle beam to compensate a deflectionof the signal charged particle beam resulting from the scanning of theprimary charged particle beam.

A deflection element configured for anti-scanning the signal chargedparticle beam may be arranged, with respect to the signal chargedparticle beam, upstream of the aperture plate, upstream of the firstlens and/or between the first lens and the second lens. Compared toanti-scanning the signal charged particle beam downstream of theaperture plate, anti-scanning upstream of the aperture plate has theadvantage that the signal charged particle beam can be more easilyaligned with a target axis. Further, anti-scanning upstream of theaperture plate may be advantageous for systems where an energy filter isprovided at the aperture plate, as the energy filter has an increasedsensitivity to the position of the signal charged particle beam withrespect to the optical axis 1103.

FIG. 1 shows a simplified side view schematic of a secondary chargedparticle imaging system. According to embodiments described herein, thesecondary charged particle imaging system includes a detectorarrangement.

The detector arrangement 1900 may include a first detection element1970, a central detection element 1950, and/or a second detectionelement 1930. The second detection element 1930 may be distanced fromthe first detection element 1970. The first detection element 1970, thecentral detection element 1950, and/or the second detection element 1930may be supported by a holder of the detector arrangement 1900. Theholder may include a holder plate on which the first detection element1970, the central detection element 1950, and/or the second detectionelement 1930 may be attached. As illustrated in FIG. 1, the firstdetection element 1970, central detection element 1950, and/or seconddetection element 1930 may be arranged, respectively, with respect tothe vertical direction, at an upper, central, and/or lower portion ofthe detector arrangement 1900. The first detection element 1970 and thefirst opening 1653 may be arranged on a first side of a reference planecontaining the optical axis 1102. The second detection element 1930 andthe second opening 1657 may be arranged on a second side of thereference plane, wherein the second side is opposite to the first side.

In addition to the first detection element 1970, the central detectionelement 1950, and the second detection element 1930, the detectorarrangement 1900 may include further detection elements. For example,the detector arrangement 1900 may include five detection elements,and/or the same number of detection elements as the number of openingsprovided in the aperture plate 1650. Each of the detection elements maybe associated with one corresponding opening in the aperture plate 1650.According to embodiments, which can be combined with other embodimentsdescribed herein, the detector arrangement 1900 includes an integernumber N of further detection elements, the integer number N eitherbeing zero or being larger than zero.

A detection element of the detector arrangement 1900, such as e.g. thefirst detection element 1970, the central detection element 1950, and/orthe second detection element 1930 may e.g. be a pin diode detector or ascintillator detector. Particularly for EBI applications, highthroughput is desired, which results in the need for very fast sensors.Accordingly, pin diode detectors can be used. The obtainable bandwidthmay depend on the size of the pin diode detector. A sensor area of 1 mm²or below may be utilized.

The first detection element 1970, the central detection element 1950,the second detection element 1930, and/or further detection elements ofthe detector arrangement 1900 may be individual detectors which may bespatially separated from each other. The individual signals obtained bythe detection elements of the detector arrangement can be combined (e.g.subtracted) to enhance contrast. Compared to e.g. detection elementswhich are arranged proximate to each other, e.g. segmented pin diodes,having spatially separated detection elements provides the advantagethat problems relating to a pin diode area which separates activesegments (e.g. charging, signal loss, cross-talk) can be more easilyovercome. Further, spatially separated detection elements are lessexpensive, have a shorter development cycle, an improved flexibility insensor design and/or a faster time-to-market.

The distance between the first detection element and the seconddetection element may be in the range from 1 to 20 mm. The distancebetween the first detection element and the central detection elementmay be in the range from 1 to 14 mm.

Compared to e.g. a bright field detector, the detector arrangement 1900including multiple detection elements, as described herein, provides anenhanced sensitivity to changes in the topography of the sample, e.g.resulting from physical defects. The multiple detection elements maycollect only secondary charged particles within certain ranges oftake-off angles at the sample. Accordingly, an enhanced contrast of theinspected features and/or defects, e.g. for defect inspection tools andreview tools or critical dimensioning tools, may be provided.

The detector arrangement 1900 may be an integrated detector arrangement.The first detection element 1970, the central detection element 1950,and/or the second detection element 1930 may be integrated into thedetector arrangement. The detection elements of the detector arrangement1900 may be separated from each other in the integrated detectorarrangement. The detection elements of the detector arrangement 1900 maybe fixedly positioned in or at the detector arrangement 1900. Thedetection elements of the detector arrangement 1900 may be fixed onto aholder or holder plate of the detector arrangement 1900.

FIG. 1 shows a simplified side view schematic of a secondary chargedparticle imaging system. According to embodiments described herein, thesecondary charged particle imaging system includes a signal chargedparticle beam 1102 and/or an optical axis 1103.

The optical axis 1103 may extend through a centre of the aperture plate230. With respect to the drawing plane of FIG. 1, the optical axis 1103extends along a horizontal (“left-right”) direction perpendicular to thevertical direction. As shown, the signal charged particle beam 1102 maytravel along the optical axis 1103. Alternatively, or in addition, theoptical axis 1103 may be of the signal charged particle beam 1102, ofthe secondary charged particle optics module 1600, of the aperture plate1650, and/or of the detector arrangement 1900.

The optical axis 1103 may extend through the central detection element1950. The optical axis 1103 may be perpendicular or substantiallyperpendicular to a plane defined by the aperture plate 1650, to a planedefined by the first lens 1612 and/or to a plane defined by the secondlens 1616. The terminology “substantially perpendicular” may refer to anangle between 90 and 110 degrees. The optical axis 1103 may be asymmetry axis of the aperture plate 1650, of the first lens 1612 and/orof the second lens 1616. The optical axis 1103 may be a symmetry axis ofthe aperture plate 1650, of the first lens 1612/and or of the secondlens 1616.

FIG. 2 shows a simplified top view schematic of a secondary chargedparticle imaging system according to embodiments described herein. Asillustrated in FIG. 2, a housing 2220 may be provided. The housing 2220may provide a vacuum containment and/or vacuum state for the signalcharged particle beam 1102. In a preferred embodiment, the housing 2220may house at least some elements of the secondary charged particleimaging system, such as the beam bender 1392, backscattered electrondetector module 1400, and the secondary charged particle optics module1600. Accordingly, the beam bender 1392, backscattered electron detectorholder 1450, backscattered electron detector element 1470, aperture1460, and/or secondary charged particle optics module 1600 may bearranged within the housing 2220. In a preferred embodiment, the beambender 1392 is arranged upstream of the backscattered electron detectormodule 1400, which in turn is arranged upstream of the secondary chargedparticle optics module 1600.

According to embodiments, an arm 2420, e.g. a rigid arm, may beprovided. The arm 2420 may be connected to and/or support thebackscattered electron detector holder 1450, backscattered electrondetector element 1470, and/or the aperture 1460. The arm may be includedin the backscattered electron detector module 1400. In an example, thearm 2420 extends into the housing 2220, extends outside the housing2220, and/or extends through a side of the housing 2220. The arm 2420may be rotatable. The arm 2420 may rotate about an axis. The axis may bearranged inside the housing 2220. The axis may be closer to a side ofthe housing 2220 than to the centre of the housing 2220. Accordingly,the backscattered electron detector module 1400, the backscatteredelectron detector holder 1450, the aperture 1460, and/or thebackscattered electron detector element 1470 may be rotatable about theaxis.

FIG. 3 shows a simplified side view schematic of a backscatteredelectron detector module and a backscattered electron detector actuatormodule according to embodiments described herein. According toembodiments, a backscattered electron detector actuator module 3440, abearing module 3260, a hinge joint slot 3424, a hinge joint pin 3422,and/or a flexible enclosure 3430 may be provided.

According to embodiments, the backscattered electron detector actuatormodule 3440 is configured for actuating, in particular moving,preferably rotating or tilting, the backscattered electron detectormodule 1400, for example, by actuating the arm 2420. The backscatteredelectron detector actuator module 3440 may include a pneumatic actuator,and/or a mechanical actuator. In another example, the backscatteredelectron detector actuator module 3440 includes a first limit stop, andoptionally a second limit stop. The first limit stop can correspond tothe first angular position 5452. The second limit stop can correspond tothe second angular position 5454. In an example, the backscatteredelectron detector actuator module 3440 is operated by a switch, such asa mechanical switch, pneumatic switch, or electrical switch. Thebackscattered electron detector actuator module 3440 may be configuredfor rotating the backscattered electron detector module 1400 and/or arm2420 between the first angular position 5452 and the second angularposition 5454. The backscattered electron detector actuator module 3440may be coupled to, integrated with, or included in the housing 2220, thebearing module 3260, the arm 2420, and/or the backscattered electrondetector module 1400. The backscattered electron detector actuatormodule 3440 may be arranged outside and/or on an outside face of thehousing 2220 and/or bearing module 3260; as part of the housing 2220,the bearing module 3260, and/or the arm 2420; and/or on an end portionof the arm 2420.

According to embodiments, the arm 2420 includes a hinge joint pin 3422.The hinge joint pin 3422 may be configured to rotate within and/or aspart of a hinge joint slot 3424. The hinge joint slot 3434 may beconnected to and/or a part of the bearing module 3260. The hinge jointpin 3433 and hinge joint slot 3434 may work as a hinge joint and/or anaxis for the rotation and/or tilt of the arm 2420 and/or backscatteredelectron detector module 1400.

According to embodiments, the flexible enclosure 3430 is configured toprovide a vacuum containment and/or vacuum state of the backscatteredelectron detector element 1470. The flexible enclosure 3430 may beconfigured to maintain the hinge joint pin 3422, hinge joint slot 3424,and/or the bearing module 3260 at an ambient pressure, state,environment, and/or condition. The flexible enclosure 3430 may becoupled, attached, and/or connected, possibly in a hermetic or sealedmanner, at a first end portion, to the housing 2220, and/or the bearingmodule 3260. The flexible enclosure 3430 may be similarly coupled,attached, and/or connected, possibly in a hermetic or sealed manner, ata second end portion, to the arm 2420 preferably between the axis and/orhinge joint pin 3422, and the backscattered electron detector element1470, the aperture 1460, and/or the backscattered electron detectorholder 1450. In an example, the flexible enclosure 3430 is a hose, abellow, is flexible and/or is suitable for vacuum use. In yet anotherexample, the flexible enclosure 3430 is a flexible bellow, providesealing between air and vacuum, maintaining the moving parts of thehinge joint pin 3422 and hinge joint slot 3424, or some rotationaljoint, and/or moving parts of the bearing module 3260 on the air side orambient side, and/or the backscattered electron detector element 1470 onthe vacuum side and/or inside the housing 2220. The flexible enclosure3430 may be pre-tensioned, preferably pre-tensioned in an assembledcondition, and preferably axially pre-tensioned. The pre-tensionedflexible enclosure 3430 may apply a force to and/or pull the arm 2420against the bearing module 3260 and/or the housing 2220. The flexibleenclosure 3430 may be suitable for enclosing at least a part of the arm2420, the hinge joint pin 3422, hinge joint slot 3424, and/or the axisof rotation of the backscattered electron detector module 1400.

According to embodiments, the bearing module 3260 is an axial bearing.The bearing module 3260 may be configured to support the arm 2420,and/or the backscattered electron detector module 1400. The bearingmodule 3260 and/or the housing 2220 may provide a reaction force to thearm 2420. The reaction force may be less than the pre-tensioning forceof the flexible enclosure 3430, with the balance provided by a vacuumforce in an operating condition and/or assembled condition. In anexample, the reaction force may be 40 N or between 0 N and 100 N. Inanother example, the pre-tensioned flexible enclosure 3430 may have apre-tensioned force of 60 N or more than the reaction force.

According to embodiments, the backscattered electron detector element1470 may have a circular, square or polygonal cross-section and/orshape. The aperture 1460 may similarly have a circular, square,triangular or polygonal cross-section.

FIGS. 4A and 4B are simplified pseudo-3D representations of an arm, ahinge joint according to embodiments described herein.

According to embodiments, the hinge joint pin 3422 and/or hinge jointslot 3424 may form a hinge joint. The hinge joint slot 3424 may be in aU-shaped slot. The hinge joint slot 3424 may be suitable to provide areaction force to the hinge joint pin 3422. The hinge joint slot may bearranged on the bearing module 3260. The hinge joint pin 3422 may bearranged on the arm 2420. The hinge joint pin 3422 may be a plurality ofpins, for example two pins, and/or arranged on diametrically oppositesides of the arm 2420. Similarly, the hinge joint slot 3424 may be aplurality of slots, for example, two slots, and/or separated by adistance at least equal to the diameter or critical dimension, or across-sectional side of the arm 2420. The hinge joint pin 3422 mayinclude a connecting angular or polygonal ring on the arm 2420. Theangular or polygonal ring may be suitable as a guide, an assemblingguide, and/or complementary face for the hinge joint slot 3424.

FIGS. 5A and 5B are simplified side view schematics of the backscatteredelectron detector module in a first angular position and second angularposition according to embodiments described herein. According toembodiments, the backscattered electron detector module 1400 and/or thearm 2420 may be switchable, rotatable, tiltable, and/or moveable betweena first angular position 5452 and a second angular position 5454. In thefirst angular position 5452, the aperture 1460 may be configured to beoperational and/or the backscattered electron detector element 1470 tobe non-operational. In the second angular position 5454, thebackscattered electron detector element 1470 may be configured to beoperational and/or the aperture 1460 to be non-operational. The firstangular position 5452 may correspond to the arm 2420, and/or thebackscattered electron detector actuator module 3440 at a first limitstop and/or a rotated-up-position/tilted-up-position. Similarly, thesecond angular position 5454 may correspond to the arm 2420, and/or thebackscattered electron detector actuator module 3440 at a second limitstop and/or a rotated-down-position/tilted-down-position. The angulardistance and/or separation between the first angular position 5452 andthe second angular position 5454 may be at least 0 degrees and/or lessthan 10 degrees, preferably in a range from 2 to 5 degrees. The rotationmay be about an axis. The rotation may be about the hinge joint pin3422.

FIGS. 6A and 6B are close-up simplified side view schematics of theaperture and backscattered electron detector element of thebackscattered electron detector module in a first angular position andsecond angular position according to embodiments described herein.According to embodiments, there may be a beam bender shield. In anexample, the beam bender shield 6394 is a high-voltage shield. The beambender shield 6394 may include a shield aperture 6396. The shieldaperture 6396 may have a circular, square, triangular, or polygonalcross-section or shape. The shield aperture 6396 may have a similar orsame cross-section as the aperture 1460 or the backscattered electrondetector element 1470. In an example, the shield aperture 6396 and/orthe aperture 1460 have a triangular shape, as shown in FIGS. 6A and 6B.In an example, the shield aperture 6396 and the aperture 1460 may be ofthe same size. In another example, at least one of the shield aperture6396 and/or the aperture 1460 have a circular shape, while the other onehas a triangular shape.

Aberrations can occur in the beam bender 1392, e.g. sector beam bender,which is used to deflect a signal charged particle beam 1102. Forexample, a hexapole component of the electric field can introduce 3-foldaberrations in the signal charged particle beam (e.g., secondaryelectron bundle) passing the sector beam bender 1392. With increasingwidth of the signal charged particle beam 1102 inside the sector beambender 1392, an increasing amount of hexapole component deforms thesignal charged particle beam 1102. An aperture, such as the shieldaperture 6396 or the aperture 1460, having a substantially triangularshaped passage area for the signal charged particle beam 1102, such as ashape of an isosceles triangle, can reduce a hexapole component of afringe field or reduce a hexapole aberration on the signal chargedparticle beam 1102. An aperture, such as the shield aperture 6396 oraperture 1460, having a substantially circular shaped passage area forthe signal charged particle beam 1102, such as in a shape of a circle,can reduce or minimize unwanted influence of deflection fields, e.g.from the sector beam bender 1392.

In a preferred embodiment, which can be combined with other embodimentsdescribed herein, the shield aperture 6396 may be upstream of theaperture 1460. The shield aperture 6396 may be triangularly shaped. Theaperture 1460 may be circularly shaped. Alternatively, at least one ofthe shield aperture 6396 and/or the aperture 1460, being positioned at adownstream side of the beam bender 1392, may have two sides, a firstside facing the beam bender 1392 being substantially circularly shapedand a second side facing away from the beam bender 1392 beingsubstantially triangularly shaped.

In some embodiments, the shield aperture 6396 may be upstream of theaperture 1460. The shield aperture 6396 may have a substantiallytriangular shaped passage area for the signal charged particle beam.Accordingly, the triangular shape of shield aperture 6396 may minimise ahexapole component of an electric fringe field. The aperture 1460 may bedownstream of the shield aperture 6396. The aperture 1460 may have asubstantially circular shaped passage area for the signal chargedparticle beam 1102. The circular shape of the aperture 1460 may minimisean influence of the electric fringe field on the signal charged particlebeam 1102. Alternatively, the aperture 1460 may have a substantiallytriangular shape passage area for minimizing an influence of thehexapole component of the electric fringe field on the signal chargedparticle beam 1102. Alternatively, or in addition, the shield aperture6396 may have a substantially circular shaped passage area for thesignal charged particle beam 1102. The circular shape of the shieldaperture 6396 may minimise an influence of the electric fringe field onthe signal charged particle beam 1102. In a preferred embodiment, whichcan be combined with other embodiments described herein, the aperture1460 has a substantially triangular shape, the shield aperture 6396 hasa substantially triangular shape, and the backscattered electrondetector element 1470 has a substantially circular shape.

In another example, the backscattered electron detector element 1470 hasa circular shape of a diameter the same as, smaller than or larger thana dimension or altitude of the aperture 1460 or the shield aperture6396. The first angular position 5452 may correspond to the operation ofthe aperture 1460 or to a secondary electron detection mode. The secondposition 5454 may correspond to the operation of the backscatteredelectron detector element 1470, or to a backscattered electron detectionmode. The first angular position 5452 and second angular position 5454are understood as one of the two possible order of the angularpositions, with the reverse order equally possible, with correspondingreversal of the relevant elements, components, operations and effects.

FIG. 7 shows a simplified side view schematic of a charged particle beamdevice according to embodiments described herein. In an example, thecharged particle beam device may be a scanning electron microscope. In afurther example, the charged particle beam device may be a multi-beamdevice. The charged particle beam device may include a charged particlebeam emitter, a beam separator, and/or an objective lens.

According to embodiments, the beam emitter 7310 is for emitting aprimary charged particle beam 7101. The beam emitter 7310 may e.g. be anelectron gun. The charged particle beam device may include an objectivelens 7370 for focusing the primary charged particle beam 7101 onto asample 7350. The charged particle beam device may include a beamseparator 7330 for separating the primary charged particle beam 7101from a signal charged particle beam 1102 emanating from the sample 7350.The charged particle beam device may include a secondary chargedparticle imaging system according to embodiments described herein. Withrespect to the propagation of the signal charged particle beam 1102, thesecondary charged particle imaging system may be arranged downstream ofthe beam separator 7330.

As shown in FIG. 7, the primary charged particle beam 7101 emitted fromthe beam emitter 7310 may travel from the beam emitter 7310 to the beamseparator 7330. As further shown, the primary charged particle beam 7101may be deflected in the beam separator 7330. As further shown, theprimary charged particle beam 7101 may travel from the beam separator7330 to the objective lens 7370 adapted for focusing the primary chargedparticle beam 7101 onto the sample 7350. According to the exemplaryembodiment illustrated in FIG. 7, the primary charged particle beam7101, when traveling from the beam separator 7330 to the sample 7350 viathe objective lens 7370, travels along the optical axis defined by theobjective lens 7370. Upon impingement of the primary charged particlebeam 7101 on the sample 7350, the signal charged particle beam 1102 isgenerated. As shown in FIG. 7, the signal charged particle beam 1102 maytravel from the sample 7350 to the beam separator 7330, wherein thesignal charged particle beam 1102 may travel in the opposite directionof the primary charged particle beam 7101. The beam separator 7330 actson the primary charged particle beam 7101 and on the signal chargedparticle beam 1102 and is adapted for separating the primary chargedparticle beam 7101 from the signal charged particle beam 1102. As shown,the signal charged particle beam 1102 may be deflected in the beamseparator 7330. The deflection may be such that the signal chargedparticle beam leaving the beam separator is directed away from theprimary charged particle beam 7101. The signal charged particle beam1102 travels from the beam separator 7330 to the secondary chargedparticle imaging system.

The beam separator 7330 may include a magnetic beam separation portion,e.g. including one or more coils, adapted for generating a magneticfield. Additionally, or alternatively, the beam separator 7330 mayinclude an electrostatic beam separation portion, e.g. including one ormore electrodes, adapted for generating an electric field. The electricfield and/or magnetic field may act on the primary charged particle beam7101 and/or on the signal charged particle beam 1102 passing through thebeam separator 7330. Under the influence of the magnetic field and/or ofthe electric field, the primary charged particle beam 7101 and thesignal charged particle beam 1102 may be deflected in the beam separator7330.

The charged particle beam device may further include at least one of thefollowing: a stage, wherein the stage may be movable with respect to theobjective lens 7370 for varying the working distance; a sample voltagesource adapted for varying the landing energy of the primary chargedparticle beam 7101; one or more proxi electrodes adapted for varying thestrength of the extraction field acting on the signal charged particlebeam 1102; a magnetic objective lens portion included in the objectivelens 7370 adapted for generating a magnetic field. As further describedabove, under the action of the controller 1630, the signal chargedparticle beam 1102 may be mapped onto the aperture plate 1650, e.g. inthe topography detection mode or in the bright field detection mode,independent of a variation of the at least one first operating parameterand/or independent of a variation of the at least one second operatingparameter.

The charged particle beam device shown in FIG. 7 includes the secondarycharged particle imaging system according to embodiments describedherein. The secondary charged particle imaging system shown in FIG. 7includes the beam bender 1392, as discussed above. As further discussedabove, the signal charged particle beam 1102 is directed away from theprimary charged particle beam 7101 by the beam separator 7330. The beambender 1392 may direct the signal charged particle beam 1102 furtheraway from the primary charged particle beam 7101, as illustrated in FIG.7.

FIG. 8 is a method diagram for operating a secondary charged particleimaging system according to embodiments described herein. According toone embodiment, a method of operating a secondary charged particleimaging system is provided. The method includes rotating a backscatteredelectron detector module between a first angular position 5452 and asecond angular position 5454 about an axis, as for example illustratedin operation 802. In embodiments, a first operational mode and a secondoperational mode can be provided by rotating the backscattered electrondetector module 1400. In the first operational mode, signal electrons orthe signal charged particle beam 1102 may pass through the backscatteredelectron detector module 1400. In the second operational mode, signalelectrons or the signal charged particle beam 1102 may impinge on thebackscattered electron detector element 1470 of the backscatteredelectron detector module 1400.

At least one of the following advantages may be realised by embodimentsdescribed herein. The backscattered electron detector can be moved inand out of the optical axis. When the backscattered electron detector ismoved out of the optical axis, the conventional secondary electrondetector with secondary electron optics can be used. By placing thebackscattered electron detector before the secondary electron optics,efficiency, in particular detection efficiency is improved, for example,up to 30%, depending on the landing energies involved. Efficiency of thebackscattered electron detection is comparable to a single beam systemwithout secondary electron optics. Another advantage is that amulti-beam system may be combined with backscattered electron detectioncapability. On-axial backscattered electron detection can be providedfor in single beam mode, for multi-beam systems or single-beam systemswith secondary electron optics. Secondary electron optics areparticularly advantageous for multi-beam systems. On-axial secondaryelectrons and backscattered electrons can be detected in one column witha simple mechanical switching. Multi-beam columns can be used fordetecting defects using backscattered electron detection. A particularadvantage is that multi-beam columns can be used in single-beam mode,secondary electron detection mode as well as backscattered electrondetection mode in a simple manner. Another particular advantage is thatthe tilting or rotating motion concept allows for the minimum spacerequirement inside, and especially outside the column. Minimal space isneeded outside of column and inside the housing. Much less space isneeded in the tilting or rotating concept as compared to a linearactuation motion. A further advantage is that by positioning thedetector after the beam bender detection efficiency and accessibilityare both optimised. Space near the primary beam may be particularlytight. Yet another advantage is that at the point after the beam bender,the electron beam can have the smallest cross-section. A smallcross-section allows for good detection efficiency. Furthermore, themoving parts are outside of the vacuum containment and contamination isavoided. This concept can be advantageous for electron beam inspectionand electron beam mask inspection.

1. A secondary charged particle imaging system, comprising: abackscattered electron detector module, wherein the backscatteredelectron detector module is rotatable between a first angular positionand a second angular position about an axis.
 2. The secondary chargedparticle imaging system according to claim 1, wherein the backscatteredelectron detector module comprises a backscattered electron detectorelement.
 3. The secondary charged particle imaging system according toclaim 2, wherein the backscattered electron detector module comprises anaperture.
 4. The secondary charged particle imaging system according toclaim 2, further comprising a beam bender.
 5. The secondary chargedparticle imaging system according to claim 3, wherein the aperture isarranged on an optical axis of a signal charged particle beam in thefirst angular position.
 6. The secondary charged particle imaging systemaccording to claim 3, wherein the aperture is arranged between the beambender and a lens system in the first angular position.
 7. The secondarycharged particle imaging system according to claim 3, wherein theaperture is configured to allow a signal charged particle beam to passthrough the aperture in the first angular position.
 8. The secondarycharged particle imaging system according to claim 1, wherein thesecondary charged particle imaging system is configured for detectingsecondary electrons in the first angular position.
 9. The secondarycharged particle imaging system according to claim 2, wherein thebackscattered electron detector element is arranged on an optical axisof a signal charged particle beam in the second angular position. 10.The secondary charged particle imaging system according to claim 4,wherein the backscattered electron detector element is arranged betweenthe beam bender and the lens system in the second angular position. 11.The secondary charged particle imaging system according to claim 2,wherein the backscattered electron detector element is configured tocollect backscattered electrons of a signal charged particle beam in thesecond angular position.
 12. The secondary charged particle imagingsystem according to claim 1, wherein the secondary charged particleimaging system is configured for detecting backscattered electron in thesecond angular position.
 13. The secondary charged particle imagingsystem according to claim 2, wherein the backscattered electron detectorelement is arranged at a point of smallest cross-section or adjacent tothe point of smallest cross-section of a signal charged particle beam inthe second angular position.
 14. The secondary charged particle imagingsystem according to claim 1, further comprising a backscattered electrondetector actuator module.
 15. The secondary charged particle imagingsystem according to claim 14, wherein the backscattered electrondetector actuator module comprises a first limit stop and a second limitstop.
 16. The secondary charged particle imaging system according toclaim 15, wherein the backscattered electron module is at the firstangular position at the first limit stop, and wherein the backscatteredelectron module is at the second angular position at the second limitstop.
 17. The secondary charged particle imaging system according toclaim 14, wherein the backscattered electron detector actuator module isconfigured for rotating the backscattered electron detector modulebetween the first angular position and the second angular position. 18.The secondary charged particle imaging system according to claim 1,wherein the backscattered electron module comprises an arm, and whereinthe arm comprises a hinge joint pin at the axis.
 19. The secondarycharged particle imaging system according to claim 1, further comprisinga flexible enclosure.
 20. The secondary charged particle imaging systemaccording to claim 19, wherein the flexible enclosure is hermeticallycoupled at a first end portion to the arm between the hinge joint pinand the backscattered electron detector element.
 21. The secondarycharged particle imaging system according to claim 19, wherein theflexible enclosure is hermetically coupled at a second end portion to ahousing.
 22. The secondary charged particle imaging system according toclaim 19, wherein the flexible enclosure is a flexible hose or bellow.23. The secondary charged particle imaging system according to claim 19,wherein the flexible enclosure is configured to maintain a backscatteredelectron detector element in vacuum condition and a hinge joint inambient condition.
 24. The secondary charged particle imaging systemaccording to claim 1, wherein an angular separation of the first angularposition and the second angular position is less than 10 degrees.
 25. Acharged particle beam device comprising the secondary charged particleimaging system according to claim
 1. 26. The charged particle beamdevice according to claim 25, wherein the charged particle beam deviceis a multi-beam charged particle beam device.
 27. A method of operatinga secondary charged particle imaging system comprising rotating abackscattered electron detector module between a first angular positionand a second angular position about an axis.